The existing transmitter for Single Carrier Frequency Division Multiplexing Access (SC-FDMA) system is shown in FIG. 1, the working process of which is as follows: the information bit stream is provided to the input end of the M-point DFT module 10 after encoding, interleaving and constellation modulation. Then the outputted data of the M-point DFT module 10 are mapped to the M allocated sub-carriers among N sub-carriers through sub-carrier mapping means 20, wherein, there are two types of sub-carrier mappings: centralized sub-carrier mapping and distributed sub-carrier mapping, and M represents the amount of sub-carriers allocated for transmitting the information. After the (N-M) unmapped sub-carriers are set to zero, the output of the sub-carrier mapping means 20 is transformed to time domain by the N-point Inverse Discrete Fourier Transform (IDFT) of the N-IDFT module 30. Then the output of the N-IDFT module 30 is inserted with Cyclic Prefixes (CP) by the CP inserting means 40, that is to say, copying the last LCP data of the N-point data group of the output of N-point IDFT to the front, wherein LCP represents the CP length. After up-sampling, Digital to Analog (D/A) conversion and carrier modulation, the signal is sent out through a single antenna.
The above-mentioned system is well recognized to be the most promising scheme in the uplink of the next generation broadband wireless communication systems. The system has the following advantages:
(1) Its peak-to-average power ratio (PAPR) is relatively low, and thus the transmitting power can be saved significantly.
(2) It avoids the multiple access interference (MAI) in the uplink of code division multiple access (CDMA) systems by providing orthogonal multi-user access.
(3) With proper time-frequency resource scheduling, it can achieve flexible traffic rate as well as frequency diversity gain or multi-user gain.
(4) With the cyclic prefix (CP) inserted in the time domain, it gives strong equalization ability in the frequency domain.
As compared with the existing wireless communication systems such as UMTS, the next generation systems are characterized by higher spectral efficiency, higher peak data rate as well as average data rate at the cell edge, and sufficient cell coverage.
For these purposes, besides obtaining the time and frequency diversity with time and frequency resource, the next generation communication systems should also make full use of the space resource to obtain the additional spatial diversity; thereby the future systems shall be equipped with multiple transmitting or receiving antennas.
In an SC-FDMA system with multiple antennas, the following two challenges should be considered carefully:
1) How to reduce the peak-to-average power ratio (PAPR) of the transmitter, especially for the uplink, i.e., the communication link from the mobile terminal (MT) to the base station (BS)? Since low PAPR amounts to high efficiency of power amplifier of MT, the lower the PAPR is, the longer the life-span of the batteries at the MT will be, or equivalently, the farther the serving distance from the MT to BS and better the cell coverage will be.
2) How to apply the space-time (ST) or space-frequency (SF) codes in the SC-FDMA systems without considerably increasing the PAPR as well as the complexity of the frequency-domain equalizer at the receiver? A simple equalizer is of great importance to the performance and complexity of the whole system. In order to obtain peak transmission rate as high as possible, broadband communication is inevitable in the next generation wireless systems, this implies that the time-domain equalization of a signal with very broad bandwidth will be quite complicated or even infeasible. Therefore, the frequency-domain equalizer is a certain choice.
Therefore, the applicant is endeavoring to achieve efficient spatial diversity for SC-FDMA systems in order to solve the two technical challenges mentioned above satisfactorily.